Soil Basics

Soils aren’t just for farmers! Soils are fundamental to every ecosystem process we know—they are the foundation of our ecosystem.  Soils provide physical support, store and cycle nutrients, regulate water quality, storage, and run-off, dictate the abundance and type of species present on the landscape, recycle organic matter, serve as filters for air, water, and organisms, and store carbon; they are also full of living creatures, bacteria, and fungi, housing innumerous species and millions of organisms.  Whether you have a farm, forest, range, or just your own garden, soils are important to you.

 

Soil is comprised of four basic components: air (~25%), water (~25%), minerals (~45%) and organic material (~5%).  The mineral component consists of sand, silt, and clay and the relative proportions of these minerals are what determine the texture, water-holding capacity, and productivity of the soil.  You may be familiar with the ‘soil triangle’, which identifies different soil types based on their percent of each sand, silt, and clay.  The most productive soils are those with a fairly even distribution of all three—called loam.nrcs soil triangle

 

Parent Material

What makes different soils have different sand, silt, and clay ratios?  Parent material is the basis of the mineral content.  Many soils have more than one parent material.  This is true in the Columbia Gorge, where ancient basalt flood-lava laid down layers hundreds of feet deep, followed by more recent volcanic lahars and, in a geologic blink of the eye, repeated scouring by the Missoula Floods. This parent material, along with organic inputs, climate, topography, biota, and time all contribute to the development of our soils.

 

 

soil_horizon

 

 

Soil horizons are the parallel layers you notice in a cross-section of your ground.  Horizons are identified beginning at surface level with the O horizon, and moving down through A, E, B and C horizons until finally arriving at the parent material, or bedrock.  The topmost horizons have the most organic matter, as vegetation both above and below ground begin to decompose.  The nutrients from the organic matter leach through the horizons with rainfall and other weathering agents, causing the color changes you can see.

 

Soil structure is another important consideration.  Soil structure refers to the aggregates of the sand, silt, and clay particles.  Soil structure can be granular, blocky, platy, prismatic, or columnar.  Soil structure plays a large role in water retention, and ultimately, productivity.

 

Your Soil

Understanding your soil type(s) will guide you in making important management decisions about your property including: what to grow and where, what types of equipment are most suitable, how much and what type of irrigation to consider, erosion and compaction hazards, productivity, and even septic suitability.

One good first step toward determining your property’s soil type is the Natural Resource Conservation Service’s (NRCS) Web Soil Survey: http://websoilsurvey.sc.egov.usda.gov/App/HomePage.htm .  This free website holds soil information for the entire country.  After selecting your Area of Interest (AOI) and viewing your basic soil type, you can navigate through the Soil Data Explorer, gathering additional information such as suitability and limitations for use for many different applications, from farming to forestry to recreation and development. 

A useful step-by-step guide to navigating the Web Soil Survey website was created by WSU Extension: http://cru.cahe.wsu.edu/CEPublications/EM064/EM064.pdf.  This guide is geared toward creating a forest plan—you may choose different objectives within the Web Soil Survey site that match your goals.

 

Soil testing is another important management tool.  Soil testing can reveal nutrient deficiencies, pH imbalances, and more.  UCD offers free soil testing for residents in Skamania and western Klickitat Counties.  Call Carly at 509-493-1936 for more information on how you can get up to four free soil tests.

 

Soil amendments can be a helpful way to increase the water-holding capacity and nutrient levels of your soils.  If you have a large area to amend, consider renting UCD’s manure spreader: http://ucdwa.org/portfolio/manure-spreader/.